Field
The present disclosure relates to a tread for a tire intended to be fitted to a passenger vehicle. More particularly, the disclosure relates to a tire that has improved performance for winter driving or driving in the wet.
Description of Related Art
Document U.S. Pat. No. 4,057,089 discloses a tread comprising a directional pattern. The “pattern” of a tread means a plurality of cuts made in this tread to a predetermined design, these cuts having a suitable width and depth. A cut generically refers either to a groove or to a sipe and corresponds to the space delimited by the walls of material facing one another and distant from one another by a non-zero distance. What differentiates a sipe from a groove is specifically this distance; in the case of a sipe, this distance is suited to allowing the opposite walls delimiting the sipe to come at least partially into contact as the sipe end of the contact patch in which the tire is in contact with the ground. In the case of a groove, the walls of this groove cannot come into contact with one another under usual running conditions.
The directional tread pattern of document U.S. Pat. No. 4,057,089 thus has a series of V-shaped grooves all pointing in the same direction all around the tread of the tire. With such a shape of tread pattern, the water is removed via the sides of the tire, improving the drainage of the contact patch in which the tire is in contact with the wet road surface and therefore improving the grip of this tire on this road surface.
Document EP0721853 discloses a directional tread pattern comprising, in addition to V-shaped grooves pointing all in the same direction, a plurality of sipes likewise all pointing in a common direction, this common direction being the opposite to the direction of the grooves. With such a configuration of tread pattern the rigidity of the tread pattern is decreased and the grip performance of the tire on a snowy road surface is improved.
With tread wear, the heights of the grooves decrease and this decreases their ability to drain water away from the contact patch. Furthermore, with this wear, the tread becomes more rigid overall. The grip performance of the tire on a wet road surface and on a snowy road surface is therefore decreased with tread wear.
The invention, in an embodiment, proposes a solution for limiting these drops in grip as the tire wears.